Resilient Packet Ring technology is a Layer 2 networking technology that defines the manner in which bandwidth is used by transmitting stations in a fiber ring network. In Resilient Packet Ring (RPR) technology, at least two counter rotating fiber ringlets couple a ring of stations, thereby allowing the stations to share available bandwidth without each station needing additional bandwidth provisioning logic.
In general, Resilient Packet Rings (RPR) permits stations, or stations, on a ring to automatically negotiate for bandwidth among themselves via a Fairness Algorithm. Each station has a topology map of the ring and can send data on the optimal ringlet towards its destination. Feedback regarding the congestion at each station is provided to each station during operation.
One feature of the RPR architecture is that it permits ‘spatial reuse’, that is, communication between different stations may occur during the same time window, since each station is using a different span of the ringlet. For example, when sending a unicast packet, the source determines which ringlet should be used based on information included in a topology map. The shortest hop count path to the destination is one method. When the packet arrives at its destination, it is removed from the ring, and thus bandwidth is consumed only on the spans between the source and the destination. The remaining spans on the ringlet remain idle, and are therefore available for use by other stations.
Because there exists the capability for spatial reuse in RPR networks, it may occur that the network is oversubscribed. Thus, stations may be advertised as capable of supporting a certain bandwidth which exceeds the instantaneous bandwidth capabilities of the network but is achievable due to the spatial reuse. In addition, certain stations may be deemed as higher priority stations than others in the network. As a result of the combination of prioritized stations and oversubscription of network resources, it may occur that some stations in the ring become starved for network resources. Various fairness mechanisms have been introduced to ensure that each station is permitted access to the network. However, the implantation of these fairness mechanisms requires feedback and computation, and therefore increases the overall complexity of the ring network. Furthermore they do not completely remove the starvation problem unless the ring bandwidth is pre-allocated or provisioned. It would be desirable to provide a base RPR transmission architecture which overcomes the starvation problems of the existing architecture for all class of traffic supported on the ring.